1. Field of the Invention
The invention relates to organosilane compounds, products and methods for their use. In particular, this invention provides water-stable organosilane compounds, products, and compositions for treating various substrates, articles treated with the compounds, products and compositions, and methods of treatment using the compounds, products and compositions.
2. Background
Organosilanes of the general formula R.sub.n SiX.sub.4-n where n is an integer of from 0 to 3, but more generally from 0 to 2 (where when n is 3 the organosilanes may only dimerize); R is a nonhydrolizable organic group, such as, but not limited to, alkyl, aromatic, organofunctional, or a combination thereof, and X is alkoxy, such as methoxy or ethoxy, are prone to self-condensation rendering such organosilanes unstable in water over commercially relevant periods of time. Additionally, X can be a halogen, such as Cl, Br, or I, and is similarly liberated as HCl, HBr, or HI. For such organosilanes, the X moiety reacts with various hydroxyl containing molecules in aqueous media to liberate methanol, ethanol, HCl, HBr, HI, H.sub.2 O, acetic acid, or an unsubstituted or substituted carboxylic acid to form the hydroxylated, but condensation-prone compound.
For organosilanes R.sub.n SiX.sub.4-n, where n is an integer from 0 to 2, hydrolysis of the first two X groups with water produces a species bearing --Si(OH).sub.2 -- units which can self-condense through the hydroxyl moieties to linear a or cyclic oligomers possessing the partial structure HO--Si--(O--Si).sub.mm --O--Si--O--Si--O--Si--OH, where mm is an integer such that an oligomer is formed. For those cases, RSiX.sub.3, hydrolysis of the third X group generates a silanetriol (RSi(OH).sub.3) which produces insoluble organosilicon polymers through linear and/or cyclic self-condensation of the Si(OH) units. This water induced self-condensation generally precludes storage of most organosilanes R.sub.n SiX.sub.4-n, where n ranges from 0 to 2, inclusive, in water. Except for some organosilanes which can be stable in very dilute solutions at specific pH ranges, the use of water solutions of most organosilanes require the use of freshly prepared solutions.
One commercially relevant example of an organosilane suffering from such undesirable self-condensation is the antimicrobial Dow Coming 5700 (Dow Coming Corporation, Midland, Mich.). The literature describes the active ingredient of Dow Coming 5700 as 3-(trimethoxysilyl)propyl-dimethyloctadecyl ammonium chloride. However, in aqueous media, it is believed that the correct active ingredient is more likely 3-(trihydroxysilyl)propyl-dimethyloctadecyl ammonium chloride. Nonetheless, 3-(trimethoxysilyl)propyl-dimethyloctadecyl ammonium chloride is a water activated antimicrobial integrated system which is capable of binding to a wide variety of natural and synthetic substrates, including fibers and fabrics, to produce a durable surface or fabric coating. 3-(Trimethoxysilyl)propyl-dimethyloctadecyl ammonium chloride is prepared by quatemization of dimethyloctadecylamine with 3-chloropropyl trimethoxysilane. See Scheme 1. ##STR1##
The C.sub.18 hydrocarbon chain quaternary ammonium portion of the molecule in Scheme 1 possesses long-acting antimicrobial properties and provides initial association with the surface of the substrate through ionic bonds and/or electrostatic interaction. Moreover, in the presence of water and as generally described above, the propyl trimethoxysilane portion of the molecule converts into a propyl trihydroxysilyl moiety and polymerizes through Si--O bonds to hydroxylated surfaces of the substrate and through intermolecular O--Si bonds. Therefore, the traditional method of use of 3-(trimethoxysilyl)propyl-dimethyloctadecyl ammonium chloride is to add a dilute solution of 3-(trimethoxysilyl)propyl-dimethyloctadecyl ammonium chloride in methanol to water. This addition rapidly converts the --Si(OCH.sub.3).sub.3 portion of the molecule into a reactive --Si(OH).sub.3 group thereby activating the molecule. The activated 3-(trihydroxysilyl)propyl-dimethyloctadecyl ammonium chloride system must then be used within a short period of time, such as a few hours to at most about 12 hours, to treat a surface or fabric to produce a permanent surface coating. Scheme 2 shows a two-stage process which is believed to represent the coating reaction. ##STR2##
First, as shown in Scheme 2, initial association of the 3-(trihydroxysilyl)propyl-dimethyloctadecyl ammonium chloride with the surface occurs either through ionic bonding between a negatively charged surface O.sup.- and the positively charged ammonium ion (if the surface is hydroxylated with acidic OH groups), or through covalent bonds between a surface OH and a --Si--OH group (if the surface possesses non-acidic OH groups), or, for non-hydroxylated surfaces, through electrostatic attraction between the negative charge that exists on most surfaces and the positively charged ammonium ion. After association of water-activated 3-(trihydroxysilyl)propyl-dimethyloctadecyl ammonium chloride with the surface, it is thought that permanent bonding to the surface occurs through a combination of additional surface OH to --Si--OH bonds with hydroxylated surfaces, and more importantly through intermolecular siloxane polymerization (--Si--O--Si-- bonds). It should be noted that it is not always the case that the trihydroxysilyl species is the moiety that binds to the substrate surface. The trimethoxysilyl species may also undergo association and/or binding to the surface and undergo polymerization with a loss of methanol. Nonetheless, once the siloxane is polymerized, the treated surface becomes permanently coated with a covalently bound octadecylammonium ion, providing a durable, long-acting antimicrobial coating that is able to destroy microbes that come into contact with the surface.
Unfortunately, as noted above, organosilanes in water, such as the activated mixture of 3-(trihydroxysilyl)propyl-dimethyloctadecyl ammonium chloride and water, are generally unstable and prone to self-condensation. For instance, the mixture of 3-(trihydroxysilyl)propyl-dimethyloctadecyl ammonium chloride and water begins to lose effectiveness in as little as four to eight hours. Gel formation in this and similar silane formulations in water begins to occur in even shorter times. The limitations of such organosilanes in aqueous media are further described in U.S. Pat. No. 5,411,585, the contents of which are hereby incorporated by this reference. Moreover, such products are notorious for agitation difficulty during the addition of the silane to water.
The use of quaternary ammonium silicon compounds as antimicrobial agents in accordance with the prior art is well known and taught in a wide variety of United States patents, e.g., U.S. Pat. Nos. 3,560,385; 3,794,736; 3,814,739, the contents of which are hereby incorporated by this reference. It is also taught that these compounds possess certain antimicrobial properties which make them valuable and very useful for a variety of surfaces, substrates, instruments and applications (see, e.g., U.S. Pat. Nos. 3,730,701; 3,794,736; 3,860,709; 4,282,366; 4,504,541; 4,615,937; 4,692,374; 4,408,996; and 4,414, 268, the contents of which are hereby incorporated by this reference). While these quaternary ammonium silicon compounds have been employed to sterilize or disinfect many surfaces, their employment is still limited because of their toxicity often as a result of the solvent system used to deliver the compound, the necessity for a solvent solution (for instance, Dow Coming antimicrobial agents contain 50% methanol), short term stability (stability of aqueous silane solutions varies from hours to several weeks only) and poor water solubility. For instance, while 3-(trimethoxysilyl)propyl-dimethyloctadecyl ammonium chloride does not suffer from water insolubility, it is unstable in water and also, because it is shipped in 50% methanol, it is overly toxic. Many other antimicrobial organosilanes, especially quaternary ammonium silicon compounds, also suffer from problems associated with physical health hazards, e.g., precautions must be taken to avoid contact with both skin and eyes, accidental spills to the surrounding area, flammability, and the added manufacturing steps needed in order to incorporate the such antimicrobial agents into other articles and surfaces, resulting in much higher manufacturing cost.
Therefore, there exists a need for extended shelf-life, water-stable organosilane compounds, products and compositions whereby, upon application, the active portion of the organosilane is operative for the selected application. Moreover, there exists a need for water-stable, organosilane compounds, products and compositions which are essentially non-toxic, non-flammable, uniformly dispersable, and simple and economical to use.